Euphroside, A New Iridoid Glucoside from Euphrasia salisburgensis HOPPE

Abstract

Five iridoid glucosides have been isolated from the whole plant of Euphrasia salisburgensis. The structure of the new compound, named euphroside, and the identity of the others have been established by chemical transformations and spectral data. Introduction. -The genus Euphrasia consists of about eighty species of which thirteen are native to Switzerland [2]. Earlier investigations on this genus are limited to the identification and/or isolation of aucubin [3] [4], catalpol [5] and melampyroside [6]. As a part of systematic isolation and structure determination of iridoid glycosides from various plants belonging to the family Scrophulariaceae we have now studied the glycosidic constituents of Euphrasia salisburgensis. Results and discussion. -Fractionation of the methanolic extract of the whole plant of Euphrasia salisburgensis gave a new iridoid glucoside, euphroside (3), along with the known glucosides boschnaloside (l), ixoroside (2), aucubin (6) and geniposidic acid (7). The structure 3 for the new compound based upon the following facts: Euphroside (3) was obtained as an amorphous powder, [a]$= -167.27' (c=O.63, MeOH) with the molecular formula C,,H,,O,,. Its UV. spectrum showed i , , , at 237 nm assigned to a conjugated enol-ether function. The IR. spectrum (KBr) of 3 showed absorption at 3360 cm-' (br., OH), 1670 cm-' and 1635 cm-' indicating the presence of an a,P-unsaturated aldehyde function.The 'H-NMR. (D20) of euphroside (3) showed two singlets at 6 9.62 and 1.62 ppm assignable to an aldehyde and a methyl group such as H3C(10), respectively. Acetylation of 3 at room temperature with acetic anhydride and pyridine gave the tetraacetate 4 which showed signals for four acetyl groups and two tertiary hydroxyl groups (exchangeable with D20). Further acetylation of 4 at room temperature with acetic anhydride and 4-dimethylaminopyridine gave the pentaacetate 5, the 'H-NMR. of which showed signals for five acetyl groups and one tertiary hydroxyl group (exchangeable with D20). The signal arising from the methyl group at 6 1.40 ppm was shifted downfield (0.18 ppm) compared to the corresponding

Iridoids. An Updated Review. Part I.

“…55 [a] -88.8°(MeOH) uv 224 (?) (400 MHz CDCI3/CD3OD) 5.42 (H-l, d, 5.8), 6.37 (H-3, d, 6.2), 4.90 (H-4, bd, 6.2), 4.83 (H-6, d, 2.2), 3.50 (H-7, d, 2.2), 2.55 (H-9, bd, 5.8), 1.44 (H-10, s), 4.62 (H-V, d, 8), 3.32 (H-2', H-5', m), (H-3', H-4', m), 3.84 (H-6', dd, 12.5, 2.5), 3.78 (H-6', dd, 12.5, 4), 4.06(H-l", bd, 7), 5.41 (H-2", bt, 7), 2.20 (H-4", bt, 7), 2.32 (H-5", bdt, 7, 7), 6.84 (H-6", tq, 7, 1.5), 1.83 (H-9", dt, 1.5, 1), 1.71 (H-10", dt, 1, 1); (CDCl,) 93.1 (C-l), 142.2 (C-3), 105.5 (C-4), 73.4 (C-5), 77.6 (C-6), 63.1 (C-7), 63.4 (C-8), 51.3 (C-9), 16.5 (C-10), 98.2 (C-V), 72.8(C-2'), 76.2(C-3'), 69.8 (C-4'), 75.9 (C-5'), 63.1 (C-6'), 58.2 (C-l"), 125.3 (C-2"), 137.1 (C-3"), 30.0 (C-4"), 26.5 (C-5"), 142.9 (C-6"), 127.1 (C-7"), 167.6 (C-8"), 12.0 (C-9"), 22.7 (C-10"). Anarrhinum oriéntale (Scrophulariaceae) (22) 30.…”

“…122.9(C-1"), 113.8(C-2"), 152.9(C-3"), l48.7(C-4"), 115.9 (C-5"), 125.2 (C-6"), 56.5 (OMe). Rehmannia glutinosa var.…”

“…2), 6.97 (H-5", d, 8.7), 7.54 (H-6", dd, 8.7, 2), 3.86 (OMe). Besseyaplantaginea (Scrophulariaceae) ( 88) 526.49 mp 216-218°uv 292,263, 226 (MeOH) (60 MHz CD3OD) 6.36 (H-3, d, 6), 2.66-2.50 (H-5, H-9, m), 4.16, 3.60 (H-10, d's, 13), 7.62-7.13 (H-2", H-5", H-6"), 3-86 (OMe); (pyridine-¿,) 94.8 (C-l), 141.8 (C-3), 102.3 (C-4), 36.5 (C-5), 81.0(C-6), 59.6(C-7), 66.9(C-8), 43.2(C-9), 60.3 (C-10), 100.0 (C-l'), 74.8 (C-2'), 78.7 (C-3'), 71.4 (C-4'), 77.9 (C-5'), 62.6 (C-6'), 166.7 (C=0), 154.5 (C-1"), -(C-2"), 150.0 (C-3"), 150.8 93.1 ( -), 141.1 (C-3), 101.8 (C-4), 35.2 (C-5), 79-3 (C-6), (C-l'), 73.5 (C-2'), 77.4 (C-3'), 70.3 (C-4'), 76.5 (C-5'), 61.5 (C-6'), 166.5 (C=0), 113.6 (Ca), 145.6 ( ß), 125.0 (C-l"), 130.5 (C-2"), 115.8 (C-3"), 159.9…”

“…15 (H-l, d, 5), 7.32 (H-3, d), 5.53 (H-6, bs),5.70 (H-7, bs), 4.30 (H-10, bs), 3.53 (COOMe), 6.15/7.43 ( , ß, d's, 16), 7.27 (H-2", d, 8),6.63 (H-3", d, 8); (DMSO-4) 95.2 (C-l), 152.2 (C-3), 108.1 (C-4),41.1 (C-5), 81.4 (C-6), 124.7 (C-7), 149.9 (C-8), 45.5 (C-9), 58.9 (C-10), 166.4 (C-ll)*, 51.0 (OMe), 98.4 (C-l'),73.1 (C-2'),77.2 (C-3'), 69.9 (C-4'), 76.5 (C-5'), 61.0 (C-6'),166.0 (0=0*,114.3 (Ca), 144.6 ^ß),125.0 (C-l"), 130.2 (C-2"),115.7 (C-3"), 159.7 (C-4"). Oldenlandia diffusa = Hedyotis diffusa (Rubiaceae) (212)5.34 (H-l, d, 5), 7.50 (H-3, s), 5.78 (H-7, m), 3.60(COOMe), 6.47/7.67(Ha, ß,d's,16),7.58 …”

8-Epiloganic Acid and 7-β-Hydroxy-8-Epiiridodial Glucoside

“…shift values has been achieved with 8-epiloganin (3). In addition, in iridoids having only a methyl group on the cyclopentane ring, the chemical shift value of the methyl appears at 16.6 ppm when it is in a-configuration (boschnaloside [13] and 19.9 ppm in 3-configuration (5-deoxystansioside [14]); therefore the value of 14.1 ppm found for 2 is in accordance with the location of the hydroxyl at C-7 (v-shielding effect 2.5 ppm) while the value of 79.4 ppm showed by the alcoholic carbon is in accordance with a trans relation with the methyl (see e.g. trans-2-methyl-cyclopentanol at 79.8 ppm [9].…”